The proposed research is concerned with the cellular mechanisms of generation and control of focal epileptogenic discharge in the brain. The effects of corticofugal epileptogenic discharge upon the activities of neurons remote from the focus will be examined in cats using microelectrode recording techniques. The phenomenon of antidromic burst generation in focal epileptogenesis will be studied in pathways connecting the two hemispheres. In addition, experiments will be done utilizing potassium-sensitive microelectrodes to measure changes in extracellular potassium concentration in the cortex during interictal and ictal seizure discharges, and to examine the mechanisms regulating concentration levels.